Message-ID: <20260122045543.218194-1-Smita.KoralahalliChannabasappa@amd.com>
Date: Thu, 22 Jan 2026 04:55:36 +0000
From: Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>
To: <linux-cxl@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<nvdimm@...ts.linux.dev>, <linux-fsdevel@...r.kernel.org>,
	<linux-pm@...r.kernel.org>
CC: Ard Biesheuvel <ardb@...nel.org>, Alison Schofield
	<alison.schofield@...el.com>, Vishal Verma <vishal.l.verma@...el.com>, "Ira
 Weiny" <ira.weiny@...el.com>, Dan Williams <dan.j.williams@...el.com>,
	Jonathan Cameron <jonathan.cameron@...wei.com>, Yazen Ghannam
	<yazen.ghannam@....com>, Dave Jiang <dave.jiang@...el.com>, Davidlohr Bueso
	<dave@...olabs.net>, Matthew Wilcox <willy@...radead.org>, Jan Kara
	<jack@...e.cz>, "Rafael J . Wysocki" <rafael@...nel.org>, Len Brown
	<len.brown@...el.com>, Pavel Machek <pavel@...nel.org>, Li Ming
	<ming.li@...omail.com>, Jeff Johnson <jeff.johnson@....qualcomm.com>, "Ying
 Huang" <huang.ying.caritas@...il.com>, Yao Xingtao <yaoxt.fnst@...itsu.com>,
	Peter Zijlstra <peterz@...radead.org>, Greg Kroah-Hartman
	<gregkh@...uxfoundation.org>, Nathan Fontenot <nathan.fontenot@....com>,
	Terry Bowman <terry.bowman@....com>, Robert Richter <rrichter@....com>,
	Benjamin Cheatham <benjamin.cheatham@....com>, Zhijian Li
	<lizhijian@...itsu.com>, Borislav Petkov <bp@...en8.de>, Smita Koralahalli
	<Smita.KoralahalliChannabasappa@....com>, Tomasz Wolski
	<tomasz.wolski@...itsu.com>
Subject: [PATCH v5 0/7] dax/hmem, cxl: Coordinate Soft Reserved handling with CXL and HMEM

This series aims to address long-standing conflicts between HMEM and
CXL when handling Soft Reserved memory ranges.

Reworked from Dan's patch:
https://git.kernel.org/pub/scm/linux/kernel/git/cxl/cxl.git/patch/?id=ab70c6227ee6165a562c215d9dcb4a1c55620d5d

Previous work:
https://lore.kernel.org/all/20250715180407.47426-1-Smita.KoralahalliChannabasappa@amd.com/

Link to v4:
https://lore.kernel.org/all/20251120031925.87762-1-Smita.KoralahalliChannabasappa@amd.com/

The series is based on branch "for-7.0/cxl-init" and base-commit is
base-commit: bc62f5b308cbdedf29132fe96e9d591e526527e1

[1] Hotplug works. After offlining the memory I can tear down the regions
and recreate them back. dax_cxl creates dax devices and onlines memory.
850000000-284fffffff : CXL Window 0
  850000000-284fffffff : region0
    850000000-284fffffff : dax0.0
      850000000-284fffffff : System RAM (kmem)

[2] With CONFIG_CXL_REGION disabled, all the resources are handled by
HMEM. Soft Reserved range shows up in /proc/iomem, no regions come up
and dax devices are created from HMEM.
850000000-284fffffff : CXL Window 0
  850000000-284fffffff : Soft Reserved
    850000000-284fffffff : dax0.0
      850000000-284fffffff : System RAM (kmem)

[3] Region assembly failure works same as [2].
Before:
2850000000-484fffffff : Soft Reserved
  2850000000-484fffffff : CXL Window 1
    2850000000-484fffffff : dax4.0
      2850000000-484fffffff : System RAM (kmem)

After tearing down dax4.0 and creating it back:

Logs:
[  547.847764] unregister_dax_mapping:  mapping0: unregister_dax_mapping
[  547.855000] trim_dev_dax_range: dax dax4.0: delete range[0]: 0x2850000000:0x484fffffff
[  622.474580] alloc_dev_dax_range: dax dax4.1: alloc range[0]: 0x0000002850000000:0x000000484fffffff
[  752.766194] Fallback order for Node 0: 0 1
[  752.766199] Fallback order for Node 1: 1 0
[  752.766200] Built 2 zonelists, mobility grouping on.  Total pages: 8096220
[  752.783234] Policy zone: Normal
[  752.808604] Demotion targets for Node 0: preferred: 1, fallback: 1
[  752.815509] Demotion targets for Node 1: null

After:
2850000000-484fffffff : Soft Reserved
  2850000000-484fffffff : CXL Window 1
    2850000000-484fffffff : dax4.1
      2850000000-484fffffff : System RAM (kmem)

v5 updates:
- Patch 1 dropped as its been merged for-7.0/cxl-init.
- Added Reviewed-by tags.
- Shared dax_cxl_mode between dax/cxl.c and dax/hmem.c and used
  -EPROBE_DEFER to defer dax_cxl.
- CXL_REGION_F_AUTO check for resetting decoders.
- Teardown all CXL regions if any one CXL region doesn't fully contain
  the Soft Reserved range.
- Added helper cxl_region_contains_sr() to determine Soft Reserved
  ownership.
- bus_rescan_devices() to retry dax_cxl.
- Added guard(rwsem_read)(&cxl_rwsem.region).

v4 updates:
- No changes patches 1-3.
- New patches 4-7.
- handle_deferred_cxl() has been enhanced to handle case where CXL
  regions do not contiguously and fully cover Soft Reserved ranges.
- Support added to defer cxl_dax registration.
- Support added to teardown cxl regions.

v3 updates:
 - Fixed two "From".

v2 updates:
 - Removed conditional check on CONFIG_EFI_SOFT_RESERVE as dax_hmem
   depends on CONFIG_EFI_SOFT_RESERVE. (Zhijian)
 - Added TODO note. (Zhijian)
 - Included region_intersects_soft_reserve() inside CONFIG_EFI_SOFT_RESERVE
   conditional check. (Zhijian)
 - insert_resource_late() -> insert_resource_expand_to_fit() and
   __insert_resource_expand_to_fit() replacement. (Boris)
 - Fixed Co-developed and Signed-off by. (Dan)
 - Combined 2/6 and 3/6 into a single patch. (Zhijian).
 - Skip local variable in remove_soft_reserved. (Jonathan)
 - Drop kfree with __free(). (Jonathan)
 - return 0 -> return dev_add_action_or_reset(host...) (Jonathan)
 - Dropped 6/6.
 - Reviewed-by tags (Dave, Jonathan)

Dan Williams (2):
  dax/hmem: Request cxl_acpi and cxl_pci before walking Soft Reserved
    ranges
  dax/hmem: Gate Soft Reserved deferral on DEV_DAX_CXL

Smita Koralahalli (5):
  cxl/region: Skip decoder reset on detach for autodiscovered regions
  cxl/region: Add helper to check Soft Reserved containment by CXL
    regions
  dax: Introduce dax_cxl_mode for CXL coordination
  dax/hmem, cxl: Defer and resolve ownership of Soft Reserved memory
    ranges
  dax/hmem: Reintroduce Soft Reserved ranges back into the iomem tree

 drivers/cxl/core/region.c |  58 ++++++++++++++++-
 drivers/cxl/cxl.h         |   7 ++
 drivers/dax/Kconfig       |   2 +
 drivers/dax/bus.c         |   3 +
 drivers/dax/bus.h         |   8 +++
 drivers/dax/cxl.c         |   9 +++
 drivers/dax/hmem/hmem.c   | 132 ++++++++++++++++++++++++++++++++++----
 7 files changed, 207 insertions(+), 12 deletions(-)

-- 
2.17.1

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